C and Masm program

I need to write a function funcName (int a, int b, int c) on C, which calculates the value using the formula a * b-c and returns it. Then I need to write a function on masm, which calls this function with arguments that are specified in the data segment and returns the value that the first function returns after its call. A function written in masm must be called in main and output the resulting value. I wrote a program, but when I run it, a window pops up in which it is written Unhandled exception at 0x0014000a in labvpd.exe: 0xC0000005: Access violation writing location 0x8d4e00eb. What am I doing wrong?

C code:

#include <stdio.h> 
#include <stdlib.h> 


extern "C" 
int __cdecl funcName(int a, int b, int c);

extern "C"
int FUN();


int main()
{ 
    printf("%s", "Result: ");
    printf("%d", FUN());
    scanf("%d"); 
    return 0; 


} 
extern "C" 
int __cdecl funcName(int a, int b, int c){ 
    int result = a*b-c;
    return result;
}

MASM code:

.686 
.MODEL C, FLAT
.STACK 
.DATA
a dw 10
b dw 20
d dw 30
.CODE 

EXTRN funcName : proc

FUN PROC
push d
push b
push a
call funcName
ret
FUN ENDP
END